Heat exchangers described in Japanese Utility Model Application Laid-open No.4-82857 and Japanese Patent Application Laid-open No.58-205091 are known which include a plurality of heat-transfer plates disposed in parallel at a predetermined distance, and plates are brazed to end faces of the heat-transfer plates to define fluid passages.
When partition walls for partitioning combustion gas passage inlets and outlets from air passage outlets and inlets are formed by the plates brazed to the end surfaces of the heat-transfer plates, a load is applied to the plates due to a pressure differential between a combustion gas and air. For this reason, there is a possibility that a stress may be concentrated on brazed portions of the plates and the end surfaces of the heat-transfer plates, resulting in a reduced durability.